When a mobile device (e.g., cell phone, UE) with an active/ongoing communication connection (e.g., voice or data call) is moving away from the coverage area of a first cell and entering the coverage area of a second cell, the communication connection is transferred to the second cell (target cell) in order to avoid link termination when the phone gets out of coverage of the first cell (source cell). This “transfer of a connection” is termed handover (or handoff). There may also be other reasons for performing a handover, such as load balancing.
Conventionally, a UE is configured by the mobile network operation (MNO) to perform measurements on downlink signals of various cells usually comprising its own serving cell as well as neighboring cells (of the same RAT, or of a different RAT). The MNO may also configure some reporting details (e.g., trigger events, frequency layer, thresholds, periodicity, etc.) in the UE. The UE in turn is to report its findings to the infrastructure. The final handover decision is taken by the infrastructure side (e.g., by the base station currently serving the UE).
Some new use cases are currently under discussion in 3GPP's RAN working groups (WGs) are dealing with “small cell enhancements” and “dual connectivity”. The concept of small cells is about deployment of additional low power nodes under macro layer coverage for capacity extension and coverage improvement purposes. The term “dual connectivity” refers to an operation where the UE consumes radio resources provided by at least two different base stations. In the context of “small cell enhancements” the first base station may be a macro eNB providing a macro cell with basic coverage, while the second base station may be a pico/femto eNB providing a small cell with additional capacity or coverage. One issue with this situation is that due to the low power nature of the additionally deployed small cell nodes, handover decisions performed in the conventional manner may be less than optimum.
Thus there are general needs for base stations and methods for making improved more optimum handover decisions, particular in small-cell deployment scenarios.